1. Field of the Invention:
The present invention is in the field of vacuum interrupters generally and is specifically directed to vapor or condensing shields for vacuum interrupters.
2. Description of the Prior Art:
It has been customary in the design of vacuum-type circuit interrupters, to provide a vapor or condensing shield to prevent the outward dissemination of metallic particles during arcing and their concomitant deposit on the inner walls of the outer insulating casing, which may be, for example, of glass or ceramic material. Consequently, practically all vacuum-type circuit interrupters have such condensing shields.
Some of the shields may be disposed at the potential of one of the separable contacts, as in U.S. Pat. Nos. 2,975,256, Lee et al, or 3,244,842, Kameyama et al. Other condensing shields may, for example, be at a floating potential, such as set forth in U.S. Pat. No. 3,592,987, Lempert et al.
U.S. Pat. No. 4,020,304 teaches a vacuum type circuit interrupter having a vapor or condensing shield comprised of two materials.
The central portion of the vapor shield, that portion of the shield exposed to the arc, consists of a high conductivity material, for example copper, and the end portions of the shield are comprised of a high voltage material such as stainless steel, steel, nickel, aluminum and an alloy containing approximately 66%, by weight, nickel and 31%, by weight copper. This alloy is sold commercially under the Trademark Monel.
The central copper portion is brazed to the second metal, for example, stainless steel.
In FIG. 3 of U.S. Pat. No. 4,020,304, a shield is shown in which the stainless steel portion of the shield extends the whole length of the shield and a copper portion is brazed to the steel portion only in the arcing area.
Such a structure as that shown in FIG. 3 of the U.S. Pat. No. 4,020,304 has the shortcoming that a high electrical field and a field emission is established between the contacts of the interrupter and the shield at the point where the copper portion ends.